A stabilizer link is a stabilizer link part connecting a suspension apparatus and a stabilizer apparatus. FIG. 1 is a perspective view showing a schematic structure of front wheel side of vehicle. Each suspension apparatus 10 is provided at left and right tires 30 and has an arm 11 and a cylinder 12. A lower end portion of the arm 11 is fixed at a bearing portion which supports a shaft of the tire 30. The cylinder 12 is elastically movable relatively to the aim 11. A bracket 13, to which a stabilizer link 1 is mounted, is provided at the arm 11. The suspension apparatus 10 supports the weight of vehicle body which is applied to the tire 30. A stabilizer apparatus 20 is equipped with a bar 21 which is approximately U-shaped, and the stabilizer apparatus 20 is mounted to the vehicle body via bushes 22. The stabilizer apparatus 20 secures roll stiffness of vehicle.
The stabilizer links 1 are provided at the bracket 13 of the suspension apparatus 10 and at the end portion of the bar 21 of the stabilizer apparatus 20. The stabilizer links 1 are connected to each other by a support bar 6. The stabilizer link 1 transmits a load, which is generated when the suspension apparatus 10 receives an input from a road surface, to the stabilizer apparatus 20.
FIG. 2 is a side sectional diagram showing a specific example of structure of the stabilizer link 1. The stabilizer link 1 is equipped with a stud ball 2, a ball seat 3, a housing 4, and a dust cover 5.
The stud ball 2 has a stud portion 2A and a ball portion 2B which are integrally formed. A screw portion 2C is formed at a leading end portion of the stud portion 2A. The screw portion 2C of the stabilizer link 1 proximate to the suspension apparatus 10 is fixed at the bracket 13 of the arm 11 by screw fastening, and the screw portion 2C of the stabilizer link 1 proximate to the stabilizer apparatus 20 is fixed at the bar 21 by screw fastening. The ball seat 3 and the housing 4 form a pivot support member which universally supports the stud ball 2.
The ball portion 2B of the stud ball 2 is press-fitted into a concave portion 3A of the ball seat 3, and the concave portion 3A of the ball seat has a bearing function. The housing 4 holds the ball seat 3 therein. The dust cover 5 prevents foreign objects from entering the concave portion 3A of the ball seat 3. The support bar 6, which connects the stabilizer links 1, is provided at a side surface of the housing 4. A thermal caulking portion 3B, which is used as a fixing portion, is formed at a bottom portion of the ball seat 3. In formation of the thermal caulking portion 3B, a pin portion of the ball seat 3 is projected from a hole portion 4A of the housing 4 to an external portion, and the pin portion is deformed by thermal caulking or ultrasonic caulking, so that the deformed pin portion is caulked to the outside of the housing 4. The ball seat 3 is fixed to the housing 4 by the thermal caulking portion 3B (for example, Patent Documents 1 and 2).
In this stabilizer link 1, in order to prevent removal of ball portion 2B of the stud ball 2 from the concave portion 3A of the ball seat 3, it is necessary that pull-out strength be increased. In this case, the strength of the thermal caulking portion 3B, which is a portion for fixing the ball seat 3 to the housing 4, corresponds to the strength of the ball seat 3 made of the same material, so that pull-out strength of the stud ball 2 is determined by the strength of the ball seat 3.
It is thought that a reinforced resin including a reinforcing agent (glass fiber or the like) is used for the ball seat 3 in order to increase the strength of the ball seat 3. However, in this case, the reinforcing agent may have characteristics of attack to the ball portion 2B of the stud ball 2, so that the bearing function of the ball seat 3 may be deteriorated. On the other hand, when polyoxymethylene (POM), which does not include a reinforcing agent, is used as a material of the ball seat 3 in order to prioritize the bearing function, for example, only the pull-out strength of about 2000N to 2800N may be obtained in use of a ball portion of φ16.
The inventor has proposed a hybrid type ball seat obtained by two-color molding in order to realize both increase in pull-out strength and prevention of bearing function deterioration (for example, Patent Document 3). The hybrid type ball seat has a ball receiving portion and a reinforcing portion. The ball receiving portion has a bearing function for universally supporting a ball portion of a stud ball. The reinforcing portion is formed at the outside of the ball receiving portion and made of a reinforced resin.
Patent Document 1 is Japanese Unexamined Patent Application Publication No. Hei 6-117429, Patent Document 2 is Japanese Unexamined Patent Application Publication No. Hei 7-54835, and Patent Document 3 is Japanese Unexamined Patent Application Publication No. 2010-65725.